Steel Plastic Composite Pipe

The steel-plastic composite pipe is a product based on a steel pipe and coated with a plastic anti-corrosion layer on its inner and outer surfaces or inner and outer surfaces. It is also called a composite plastic steel pipe.

Steel-plastic composite pipes are made of seamless steel pipes and welded steel pipes. The inner wall is painted with high adhesion, anti-corrosion, food-grade hygienic polyethylene powder coating or epoxy resin coating. The galvanized inner-coated plastic composite steel pipe for water supply is made through pretreatment, preheating, inner coating, leveling, post-treatment and other processes. It is an upgraded product of the traditional galvanized pipe. Steel-plastic composite pipes are generally connected by threads, grooves, and flanges.

The core advantages of steel-plastic composite pipes are reflected in the following aspects:
Steel pipe strength + plastic corrosion resistance: It combines the mechanical strength, rigidity, and impact resistance of steel pipes with the corrosion resistance, wear resistance, and low water flow resistance of plastic pipes.
Hygienic and non-toxic: The smooth inner wall prevents scaling and microbial growth, ensuring the fluid is not subject to secondary contamination and meets national food hygiene standards.
Long service life: Service life can reach up to 50 years.
Low overall cost: It can replace stainless steel pipes, rubber-lined pipes, glass-lined pipes, and other precious metal pipes.

Steel-plastic composite pipes can be classified in several ways, including by composite process, location of the plastic layer, and application.
1. Classification by Composite Process: Steel-plastic composite pipes are mainly divided into two categories based on the bonding process between the plastic and the matrix:

The main processes for plastic-lined steel pipes include:
Inner plastic lining process: After applying adhesive to the outer wall of a plastic pipe, it is placed inside a steel pipe, allowing the plastic to expand upon heating and form a composite.
Rotational molding process: Plastic powder is melted and molded onto the inner wall of a steel pipe through rotational heating.

The main processes for plastic-coated steel pipes include:
After pretreatment and heating of the steel pipe, epoxy resin or polyethylene powder is coated using electrostatic adsorption or spraying, followed by high-temperature curing.

2. Classification by the location of the plastic layer

3. Classified by purpose

4. Classified by plastic material

Core Performance Characteristics
1. Excellent Corrosion Resistance: The inner and outer plastic layers of the steel-plastic composite pipe provide corrosion protection. It can be used in environments ranging from -40°C to 120°C and is resistant to most acids, alkalis, and salts, except for concentrated nitric acid, fuming sulfuric acid, chlorosulfonic acid, and strong oxidants. Its corrosion resistance lifespan is consistent with galvanized pipes, reaching up to 30 years.
2. Hygienic and Environmentally Friendly: The smooth inner wall of the steel-plastic composite pipe prevents scaling and microbial growth, ensuring the fluid is not subject to secondary contamination. It is hygienic and non-toxic, meeting national food hygiene standards.
3. High Strength and Good Mechanical Properties: The steel-plastic composite pipe retains the mechanical strength of steel pipes while possessing the corrosion resistance of plastic pipes. Its tensile, bending, and impact resistance indicators are close to those of Q235 steel pipes. Its service life is 4-5 times that of ordinary steel pipes.
4. Low Fluid Resistance: The smooth inner wall of the plastic lining has a lower thermal conductivity than other materials, resulting in low fluid resistance and no scaling.
5. Bond Strength
One of the key performance indicators of steel-plastic composite pipes is the bond strength between the plastic layer and the base pipe:
Plastic-lined composite steel pipe: The bond strength between the in
Spiral seam plastic-lined composite steel pipe: The peel strength should be no less than 35N/cm.
Coating adhesion: Epoxy coating ≥4MPa, polyethylene coating ≥3MPa.
6. Applicable Pressure and Temperature
GB/T 28897-2021 specifies the maximum working pressure and maximum working temperature of steel-plastic composite pipes in Appendix A. Different specifications and materials of steel-plastic composite pipes have different applicable pressures:
Small diameter pipes (DN20-DN50): Maximum pressure up to 2.5MPa
Medium and large diameter pipes (DN63-DN250): Maximum working pressure is 2.0MPa
Large diameter pipes (DN300-DN400): Maximum working pressure is 1.6MPa

Application of steel-plastic composite pipe
1. Various forms of circulating water systems (civil circulating water, industrial circulating water), excellent performance, anti-corrosion life up to 50 years.
2. Fire water supply system.
3. Water supply and drainage transportation of various buildings (especially suitable for cold and hot water systems in hotels, hotels, and high-end residential areas).
4. Various chemical fluid transportation (acid, alkali, salt corrosion).
5. Buried pipes and passing pipes for wires and cables.
6. Ventilation pipes, water supply and drainage pipes of mines and mines.
The steel-plastic composite pipe is extensively applied to the civil water supply, industrial water supply, fire fighting, sewage transportation, communication circuit, optical fiber cable, coal gas transportation, foodstuff process, medicine and machinery fields, especially an ideal product for the urban water supply.

The steel-plastic composite pipe is extensively applied to the civil water supply, industrial water supply, fire fighting, sewage transportation, communication circuit, optical fiber cable, coal gas transportation, foodstuff process, medicine and machinery fields, especially an ideal product for the urban water supply.

Steel-plastic composite pipe Chinese, British, American and Japanese national standards：

Chinese standard:

GB/T 28897-2021 "Steel-plastic composite pipes and fittings for fluid transportation"

American standard:

ASTM F2880, a standard developed by the American Society for Testing and Materials (ASTM), specifies dimensional, quality, and performance requirements for steel-plastic composite pipe and fittings. This is a comprehensive standard, including the material, manufacturing process, test method, marking and other content of the pipe fittings, which is a relatively common standard in the world.

British Standard:

BS 6920-1:2014, this standard mainly covers the applicability of non-metallic products in contact with human drinking water, including steel-plastic composite pipes, etc., to ensure that these products will not have adverse effects on water quality.

Japanese standard:

JIS K 6741-1999, this standard specifies the requirements for unplasticized polyvinyl chloride (PVC-U) pipe fittings, including steel-plastic composite pipes. The JIS K 6741-1999 standard covers the dimensions, physical properties, chemical resistance and other requirements of pipe fittings to ensure that the quality and performance of products meet the requirements of Japan.

This document specifies the classification and code, order content, size, weight and tolerance, technical requirements, test methods, inspection rules, packaging, marking, quality certificate, transportation and storage of steel-plastic composite pipes and pipe fittings for fluid transportation.

The specifications of steel-plastic composite pipes are expressed in "nominal diameter (DN)" or "outer diameter × wall thickness".

Common Specifications Comparison Table

The size of the steel-plastic composite pipe varies according to the specifications
The specification is 15*1.8mm, the outer diameter is 20.5mm, and the wall thickness is 1.8mm;
The specification is 15*2mm, the outer diameter is 20.8mm, and the tube wall thickness is 2mm;
The specifications can reach 150*4.5mm, the outer diameter can reach 165mm, and the wall thickness is 4.5mm.